Fluid filters are commonly used in a variety of applications, including hydraulic systems, fuel systems and lubrication systems. Such filters generally include a filter element enclosed within a housing and mounted on a filter head. The filter head is usually incorporated into a fluid line of the flow system. Thus, the fluid head generally includes an inlet port, whereby fluid flow is received and directed into the filter or filter assembly. The filter head also generally includes outlet means by which fluid is received from the filter assembly, following filtration, and is directed back into a fluid flow-line.
Frequently used filter or filter assemblies are of the spin-on type, such as the one described in U.S. Pat. No. 4,369,113, incorporated herein by reference. The filter head assembly of the present invention is particularly adapted for use with such spin-on filters; however the principles may be employed with other types of filter systems.
Generally, such filter assemblies provide for the removal of undesired particles from a fluid line. Eventually, the filter elements of such assemblies may become clogged, prohibiting substantial fluid flow across the filter element. When such condition occurs, pressure on the upstream side of the filter assembly, relative to the downstream side, may become substantial. Also, the volume of fluid flow from the outlet end would become reduced and quite possibly could be entirely stopped.
The above type of blockages in fluid flow lines can pose numerous problems. For example, should fluid flow outward from the filter head at an appropriate rate substantially stop, then machinery located downstream may become damaged. Further, the increased pressure on the upstream side of the filter may result in rupturing of fluid seals, or damage to machinery located upstream of the filter. Also, should the upstream pressure become great enough, the filter itself may rupture or collapse, possibly resulting in a release of undesired matter from the filter, which can damage downstream equipment or occlude fluid lines.
To alleviate some of the above-described problems, a filter system may include a bypass line, operated by means of a relief valve, to permit fluid flow to selectively circumvent the filter in response to substantial occluding or plugging of the filter assembly. While numerous arrangements are possible, generally such bypass lines are of two basic types. In the first, when substantial plugging of the filter occurs, the relief valve permits fluid flow to merely circumvent the filter, and lead back into the main fluid line. For this type of arrangement, the fluid flowing into the downstream machinery will not have been filtered; however, at least downstream machinery will be protected from loss of substantial fluid pressure.
For the other type of arrangement, generally the relief valve operates to permit fluid flow into a line which is directed back to a fluid reservoir or elsewhere. While downstream equipment may not be protected under such circumstances, at least the filter assembly and any upstream equipment are protected from substantial increases in pressure. Also, such an arrangement may be useful when downstream machinery can tolerate a reduction in fluid flow, but not unfiltered fluid.
Conventional relief valves may be of numerous types. Generally, a differential valve may be used to sense the pressure differential between the upstream and the downstream sides of the filter. Should the pressure of the upstream side relative to the downstream side become sufficiently great, such a valve would open, permitting a circumventing flow of either of the two types described above. This type of valve generally includes a valve member therein which receives upstream and downstream pressure against opposite ends or sides thereof. Should the pressure of the upstream side increase relative to the downstream side, such a valve member will move within the valve body, generally opening a flow passageway for fluid to escape through an auxiliary or outlet line.
Generally, for conventional arrangements, the valve body defines a longitudinal chamber in which the piston member is slidably retained. The longitudinal chamber has a first end in communication with an upstream side of the filter assembly, and a second end in communication with the downstream side of the filter assembly. The valve member, again, is positioned between the two inlet ends of the valve chamber, and is slidable therebetween.
Conventional relief valves are generally designed to include a mechanical or electrical indicator to produce an output signal, either visually or electrically, that the filter element is plugged.
In addition to relief valves, conventional filter designs also include a separate integrated device for fluid bypass. The differential pressure relief valve opens to prevent damage to the system from excess differential pressure.
As indicated previously, generally the filter assembly is attached to a filter head by conventional means such as those described in U.S. Pat. No. 4,369,113. Such filter heads are preferably die-cast as a single unit, with appropriate lateral bores or holes drilled therein following the casting, to provide for attachment to a fluid line and to filter means. It would be preferred that a relief valve body and bypass valve be capable of being cast directly into the filter head at the time of the filter head assembly; for convenience, for reduction of expense; and for efficiency of operation without substantiated risk of leakage. However, previous filter heads have not generally provided for this, especially in arrangements wherein the valve body has means correcting for the problems described above.
Generally, what has been needed has been a relief valve assembly that produces a discreet signal that a filter has become clogged and that the discreet signal will meet the requirements for use in microprocessor controlled systems. This necessitates isolation of a pressure to actuate the switch, controlled by the differential pressure across the filtering medium and independent of fluctuations in system pressure. Also, what is needed is a device which incorporates the pressure isolation and fluid bypass into one device. As will be seen, the instant invention includes such means, and other advantageous improvements.